1. Field of the Invention
The present invention relates to a liquid shut-off valve and, more particularly, to a liquid shut-off valve which is capable of shutting off a flow of a liquid with a small valve actuating power.
2. Description of the Related Art
Various types of liquid shut-off valve have been known such as a diaphragm-actuated liquid shut-off valve and a solenoid-actuated liquid shut-off valve.
In general, a diaphragm-actuated liquid shut-off valve has a diaphragm which separates two chambers from each other. A valve member extends from one side of the diaphragm through one of the two chambers for cooperation with a valve seat which is formed in a liquid pipe. The diaphram is biased by a spring towards the other of two chambers so as to keep the valve member away from the valve seat when no signal pressure is applied to the other of two chambers. However, when a signal pressure of a level high enough to produce a force capable of overcoming the force of the biasing spring is introduced into the other chamber, the diaphragm is deflected against the force of the biasing spring thereby bringing the valve member into engagement with the valve seat so as to close the liquid passage, thus shutting off the flow of the liquid.
On the other hand, a solenoid-actuated liquid shut-off valve is operated in accordance with an electrical signal, in contrast to the diaphragm-actuated liquid shut-off valve which operates in response to a pressure signal. Namely, a solenoid-actuated liquid shut-off valve in general has a solenoid coil and a movable core to which is fixed a valve member. When the solenoid is not actuated, the movable core is urged by a spring so as to keep the valve member in contact with the valve seat. However, when the solenoid is energized by an electrical signal current, an electromagnetic force is generated to attract the movable core against the force of the spring so that the valve member is moved away from the valve seat thereby opening the liquid passage.
Both the diaphragm-actuated and solenoid-actuated liquid shut-off valves require a large actuating power, i.e., a high pressure or a large electrical current, in order to produce a large force which overcomes the force of the biasing spring which biases the diaphragm or the movable core.